One premise underlying the benefit of exercise in weight control is that the increase in energy output is not accompanied by an equivalent increase in food intake. The objective of this project is to test this assumption. In previous prolonged studies we have shown that obese women engaged in regular exercise did not increase their food intake to compensate fully for the energy expended during the exercise; thus negtive energy balance followed. However, nonobese women who underwent a similar exercise regimen did adjust their food intake and defended their body mass. The major limitations in these previous studies on exercise and food intake were that: (1) only a small number of subjects were studied, due to the length and expense of such studies; (2) foods were varied and factors such as self-selection of different nutrients might exert an independent effect on energy intake; and (3) immediate effect of exercise on subsequent food intake were not quantified. Virtually no studies have examined the influence of acute exercise on subsequent spontaneous food intake in an adequately controlled way. We plan to monitor both exercise (mode, duration, intensity, and energy expenditure) and food intake during single course meals. With use of our computerized Eating Monitor which has been well validated, and under rigorously controlled laboratory conditions, we will study the effect of two levels of exercise on subsequent intake of a standardized, palatable test meal after two different time delays between the end of exercise and the start of the meal. Twelve obese and twelve nonobese women will each be tested four times under two levels of exercise (one or two hours of cycling at a constant power output) and two levels of time delay between exercise and the meal (15 and 75 min). Comparisons of the effects of amount of exercie, time delay, and the possible interactions, will be made between the obese and non-obese groups. Our hypothesis is that exercise will have an inhibitory effect on food intake, which will be stronger and more sustained in the obese than non-obese subjects.